About setting distance units
Release 9.1 Last modified January 25, 2006	Print all topics in : "Creating new features"

Sometimes when creating features using the editing tools in ArcMap you need to enter data that was recorded in different distance units than the coordinate system of your data.

For example, suppose your data is in a State Plane coordinate system and the linear units are U.S. Survey Feet (1 Foot_US = 0.3048006096 m). You are given measurements in international feet (1 Foot = 0.3048 m). Rather than convert all the measurements, you can type the abbreviation for International Foot, "ft", after the measurements and the tools will convert the distance correctly. You could also change the dataset coordinate system definition to use International Feet and type the distances without a unit suffix.

Whenever you are typing a distance into one of the editing tools, you have the option to specify the linear units or simply type a number, which the tool will interpret as being in the dataset's coordinate system units. Distance unit abbreviations won't work, however, if your data frame is not projected—in other words, if your data frame is not using a projected coordinate system.

The following sections outline all the distance units supported in ArcMap and describe how to implement them.

Metric units

Distance units	Abbreviation	Meters per unit	Description
Kilometer	km	1000	1,000 meters exactly
Meter	m	1	International meter
Centimeter	cm	.01	1/100 meter exactly
Millimeter	mm	0.001	1/1000 meter exactly

Imperial or international units

Distance units	Abbreviation	Meters per unit	Description
Foot	ft	0.3048	Standard foot used in the U.S. Also known as international foot or imperial foot that was used in most nonU.S. countries before the metric system.
Mile	mi	1609.344	Also referred to as a statute mile, equal to 5280 international feet.
Nautical mile	nm	1852	The nautical mile is a unit of distance used primarily in sea and aviation. The nautical mile is defined as the average distance on the earth's surface represented by one minute of latitude. In 1929, the nautical mile was defined as exactly 1852 meters, or 6076.11549 feet, a distance known as the international nautical mile.
Chain	ch	20.1168	66 international feet
Yard	yd	0.9144	Three international feet
Rod	rd	5.0292	1/4 chain, or 16.5 international feet
Link	lk	0.201168	1/100 international chain, or 66/100 international feet
Inch	in	0.0254	1/12 international foot

U.S. survey units

Distance units	Abbreviation	Meters per unit	Description
Survey foot	ftUS	0.3048006096	The U.S. survey foot is used in the State Plane Coordinate Systems. In the U.S., fundamental survey units such as rods, chains, statute miles, acres, sections, and townships all depend on the U.S. survey foot. An exact conversion to meters can be accomplished by multiplying U.S. survey feet by the fraction 1200/3937.
Survey mile	miUS	1609.3472186944	5280 survey feet
Survey chain	chUS	20.1168402337	66 survey feet
Survey rod	rdUS	5.0292100584	1/4 survey chain
Survey link	lkUS	0.2011684023	1/100 survey chain
Survey yard	ydUS	0.9144018288	3 survey feet

Conversion constants

You can use conversion constants to convert from one measurement system to another. The measurement system to be converted should be multiplied by the associated conversion constant. For example, to convert feet to centimeters, multiply feet by the conversion constant of 30.48 (27 feet x 30.48 = 822.96 centimeters).

View a table of conversion constants

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About the U.S. survey foot

In 1959, the directors of the National Bureau of Standards and the United States Coast and Geodetic Survey agreed on a redefinition of the inch–centimeter relationship. This redefinition defined 1 inch as equal to 2.54 centimeters exactly, or 1 foot as equal to 0.3048 meters exactly. However, their agreement stipulated that the older value for 1 meter equaling 39.37 inches exactly be retained for identifying the U.S. survey foot.
One of the reasons for this retention was that the State Plane Coordinate Systems, which are derived from the national geodetic control network, are based on the relationship of 1 meter equaling 39.37 inches exactly.

The difference between these two values for the foot is very small, two parts per million, which is hardly measurable, but not trivial when computational consistency is desired. Fundamental survey units, such as rods, chains, statute miles, acres, sections, and townships, all depend on the relationship of 1 meter equaling 39.37 inches exactly.
The U.S. survey foot table in the PDF represents the corrected values (or U.S. survey values), using the 39.37-inch conversion value.

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